Climbing goannas are able to overcome a trade-off in sprint speed by increasing stride frequency

Often when a species develops a performance trait that gives it an advantage in doing a particular task or surviving in a particular environment, this inhibits other performance specializations. For example, lizards that occupy open spaces on the ground would normally have a high sprint speed but may not be overly agile in comparison with arboreal species that utilise narrow branches.

Increasing stride length is an important contributor to increasing speed for lizards, and comes from holding the leg out straighter during the stride. However, increasing stride length is constrained for arboreal species, as it is associated with an increase in the height of the centre of gravity and, as a consequence, increased instability in an arboreal environment. We might therefore expect that there is a trade-off with speed for climbing lizards. Trade-offs between sprinting and climbing performance have been previously reported for diverse groups of lizards including Anolis, Chameleo and Sceloporus, but when speed was compared to climbing habitat in goannas, there was little relationship (Clemente et al. 2009).

In a recently published paper by Clemente et at (2013) it was shown that climbing goannas altered their stride frequency instead, and were therefore able to avoid the trade-off with sprint speed. Given the complexity of the kinematic changes required to alter stride frequency in goannas, it is interesting to note that these changes may have evolved at least twice independently for the climbing species.

If you would like to read a copy of the article please email Graham.

For more great biomechanics research check out Dr Chris Clemente’s work.

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